<p>the new system，which (A.uses) remote cameras (B.in the catching of) speeding motorists, (C.may undermine) the police department's authority.</p>
<p>the explaination from College Board:
There is no error at (C). The verb phrase may undermine can be singular or plural and agrees with the singular subject system.</p>
<p>WHY this :"The verb phrase may undermine can be singular or plural and agrees with the singular subject system."</p>
<p>???</p>
<p>thx</p>
<p>I’m not exactly sure what your question is, but if you’re asking why it shouldn’t be corrected to “may undermines” then you probably don’t know well about verb phrases.
Verbs Phrases are composed of two parts. Main Verb, in this case, undermine. and auxiliary or Modal verb, in this case, may. The auxiliary verbs are may, might, can, could, etc., their purpose is to express shades of time, mood and ability. Neither the subject nor the main verb is affected by the model verb: I, we, he, she, it, they can **work. we don’t say cans for singular subject and we don’t say works for singular subjects. so in your sentence, The new system… may undermine…</p>
<p>Yeah, that’s kind of a nasty one. May is a special kind of verb called modals. Modals don’t change form for different subjects. Here are the other common modals: can, could, might, must, ought to, shall, should, will, and would.</p>
<p>I don’t expect this rule to show up that often. But, the awkward and unidiomatic construction in B (in the catching of) is an issue that many writing questions test.</p>
<p>thanks. i guess i really to do some catch up on grammar~</p>
<p>thx to you too~</p>